feat: verify 'media:duration' property use valid SMIL clock values

Adds a schematron test to check that `media:duration` values are valid
SMIL clock values (based on the regex used in the Media Overlays schema
to verify `clipBegin` and `clipEnd` attribute values)

Closes #1174

src/main/resources/com/adobe/epubcheck/schema/30/package-30.sch

@@ -274,6 +274,14 @@
 
 	<!-- Media overlay checks -->
 
+	<pattern id="opf.duration.metadata.item">
+		<rule context="opf:meta[normalize-space(@property)='media:duration']">
+			<assert
+				test="matches(normalize-space(),'^(([0-9]+:[0-5][0-9]:[0-5][0-9](\.[0-9]+)?)|((\s*)[0-5][0-9]:[0-5][0-9](\.[0-9]+)?(\s*))|((\s*)[0-9]+(\.[0-9]+)?(h|min|s|ms)?(\s*)))$')"
+				>The value of the media:duration property must be a valid SMIL3 clock value</assert>
+		</rule>
+	</pattern>
+
 	<pattern id="opf.media.overlay">
 		<rule context="opf:item[@media-overlay]">
 			<let name="ref" value="./normalize-space(@media-overlay)"/>

src/test/resources/epub3/files/package-document/mediaoverlays-duration-clock-values-error.opf

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<package xmlns="http://www.idpf.org/2007/opf" version="3.0" unique-identifier="uid"
+    xmlns:dc="http://purl.org/dc/elements/1.1/">
+    <metadata>
+        <dc:title>Title</dc:title>
+        <dc:language>en</dc:language>
+        <dc:identifier id="uid">NOID</dc:identifier>
+        <meta property="dcterms:modified">2019-01-01T12:00:00Z</meta>
+        <!-- Media Overlays Duration Properties -->
+        <meta property="media:duration">0:01:30,200</meta>
+        <meta refines="#mo001" property="media:duration">0:9999:12.121</meta>
+    	<meta refines="#mo002" property="media:duration">45mon</meta>
+    </metadata>
+    <manifest>
+        <item id="t001" href="contents_001.xhtml" properties="nav" media-type="application/xhtml+xml"/>
+        <item id="mo001" href="mediaoverlay_001.smil" media-type="application/smil+xml"/>
+    	<item id="t002" href="contents_002.xhtml" media-type="application/xhtml+xml"/>
+    	<item id="mo002" href="mediaoverlay_002.smil" media-type="application/smil+xml"/>
+    </manifest>
+    <spine>
+        <itemref idref="t001"/>
+    </spine>
+</package>

src/test/resources/epub3/mediaoverlays-package-document.feature

@@ -59,3 +59,12 @@ Feature: EPUB 3 ▸ Media Overlays ▸ Package Document Checks
     Then error RSC-005 is reported
     And the message contains "must not be used with the media:playback-active-class property"
     And no other errors or warnings are reported
+
+  Scenario: Report 'media:duration' properties with non-clock values
+    When checking file 'mediaoverlays-duration-clock-values-error.opf'
+    Then the following errors are reported
+      | RSC-005 | must be a valid SMIL3 clock value |
+      | RSC-005 | must be a valid SMIL3 clock value |
+      | RSC-005 | must be a valid SMIL3 clock value |
+    And no other errors or warnings are reported
+